1. Field of the Invention
This invention relates to solid state power controllers, and more particularly to an application in which power to two loads, such as a combined ceiling fan and light fixture, is individually controlled from a wall mounted double control fixture connected to the ceiling fixture by a conventional two conductor cable.
2. Description of the Prior Art
The invention seeks to find a simple way of reducing the cost of installing a combined ceiling fan and light fixture. The installation costs are particularly severe in situations where the electrical connection boxes and electrical cable between the boxes and to an ac line are already installed in finished partitions and have an insufficient number of conductors for the new installation. If, for instance, the new cabling between boxes requires only two conductors, then the original cabling can usually be reused, and the cost of installation greatly reduced.
The principal methods of controlling plural remote loads in response to control signals conducted over a single communication path have been stepping relays, which can be caused to step to successive switching states upon closure of a single switch. A related approach for load selection, also analogous to a conventional three-way switch, is disclosed in U.S. Pat. No. 4,322,632, Hart et al. A somewhat similar method has been used in model trains, as for instance, the reversing solenoid normally having only two positions, used to permit a toy train engine to run in the forward or reverse sense by the mere reapplication of power. This operation requires no control conductors in addition to the two principal energization conductors but permits power adjustment to the load in either forward or reverse operation of the motor.
In electronic applications, signal routing has conventionally employed "steering diodes", so that it is not unknown that a reduction in conductors may be accomplished by letting the polarity of the control signal permit routing of a signal carried by a single conductor to two different control signal responsive devices. In most wired systems, a single communication path requires a return path in addition to the outgoing path, and this requires two conductors. Thus, when steering diodes are employed, a third conductor for the "ground return" is normally available. This ground return tends to be overlooked in complex circuits, where a large number of circuits share the ground return.
Returning, however, to the application at hand, that is to say, the application of controllable amounts of power to two remotely energized loads--i.e., a combined light and fan--from an ac source, neither of the existing approaches, unmodified, provide an on-off control of each load circuit, adjustment of the amount of power applied to each load, and at the same time the necessary cabling to make power initially available at either the controller or at the load, available at both the controller and the load.